J 593 
S94 
"opy 1 



Quantitative Relationships of Carbon, 
Phosphorus, and Nitrogen in Soils 



PRESENTED TO THE 



FACULTY OF THE UNIVERSITY OF ILLINOIS 

URBANA, ILLINOIS, U. S. A, 



AS A 



Thesis for the Degree of Doctor of Philosophy 

JUNE, 1909 



BY 



ROBERT STEWART, B. S. 



PUBLISHED BY 

THE UNIVERSITY OF ILLINOIS 

AGRICULTURAL EXPERIMENT STATION 

AS BULLETIN No. 145 



UNIVERSITY OF ILLINOIS 



Agricultural Experiment Station 



BULLETIN NO. 145 



QUANTITATIVE RELATIONSHIPS OF 

CARBON, PHOSPHORUS, AND 

NITROGEN IN SOILS 



Bv ROBERT STEWART 




URBANA, ILLINOIS, APRIL, 1910 



f 

1« A Hi 



( iTti. \y«rs I "f \j 



Note 






Ivohcrl v^tewart was born in American Fork, Utah, August 16, 
1S77. Me secured his common school education in the pubhc 
schools of rtah. In the fall of 1896 he entered the preparatory 
department of the Ag-ricultural College of Utah. He graduated 
from this institution in June, 1902, with the degree of Bachelor of 
vScience. He immediately received an appointment as assistant 
chemist in the Utah Experiment Station. While holding- this po- 
sition, during the years 1902-03, 1903-04, he took graduate stu- 
dent work in. the college. During the school year 1904-05 he was 
a member of the Graduate School of the University of Chicago 
where he studied chemistry under the direction of Doctor Nef. In 
i()05 he was ap])ointed assistant professor of chemistry in the Utah 
College and while holding tliis position, during the years 1905-06, 
i9of>-0/, 1907-08, he continued his graduate student work. Dur- 
ing the summer of i<jo6 he was a member of the Graduate School 
of Agriculture held at the University of Illinois. In June, 1908, 
he was aj:)pointed professor of chemistry in the LUah Colleg'e and 
was granted a lea\e of absence to carry on graduate work at the 
L'nixersity of Illinois. 

He is the senior author of lUilletin 103, "Milling- Qualities of 
Utah Wheat," and lUilletin 106, ".\ vStudy of the Influence of Irri- 
gation Waters upon the Movement and I'roduction of Nitrates in 
the Soil," which lias been accepted for publication by the Utah F.x- 
periment Station. 

During the scliool year 1908-C9 he held a fell()wship in agron- 
oniv in tlie l^ni\ersitv of Illinois. He is a member of the Illinois 
clia])ler of Sigma Xi and also a charter member of the Illinois 
cliapter of tlie American Society of Agronomy. 



QUANTITATIVE RELATIONSHIPS OF 
CARBON, PHOSPHORUS AND 
NITROGEN IN SOILS* 



By ROBERT STEWART 



(A) HISTORICAL RtiSUMri 

The literature on carljon, nitrogen and phosphorus "in soils is 
voluminous. The resume given herewith by no means attempts to 
include all that pertains to these elements in the soil, l)ut it is con- 
fidentlv believed that it fairly represents the literature pertaining 
to tliis particular phase of the sul)ject. 

I. Carbon in Soils 

Carbon m^x exist in soils as inorganic and organic carbon. The 
agricultural \alue of org-anic carbon, or org-anic matter, of soils 
has long been recognized by the practical husl)andman, and the 
scientific man early recognized its value when the applications of 
science were made to agricultural problems. 

Miilder ( i ) in 1844, made an elaborate study of the organic 
matter of the soil, and seems t(^ have l>een the first one to sug'g'est 
that it consisted of other elements than carbon, hydrogen and 
oxygen. He separated the org-anic matter into xarious supposed 
pure org'anic compounds of an acid nature, which were analyzed 
and studied by the usual organic method. 

Wolff (2) determined the org-anic matter of the soil bv calcu- 
lation, l)v use of the factors 1.724 or 0.471 : he multiplied the or- 
g'anic carbon 1)y the fonner factor, or the totid organic carl)on 
dioxid by the latter. The factors were derived from the concep- 
tion tliat "Inimus" contained 5<S percent carbon. 

Detmer (9) attempted to isolate "pure" humic acid from the 
soil and to study its properties, fie obtained a fairlv pure product 
which he studied and submitted to analvsis. 

A little later Grandeau (10) developed his well known method 
for detemiining the iiiuticrc noire of soils, which he regarded as 
of great importance. He stated that soils owed their color and 

*Submitted to the FacuUv of th? Graduate School of the Universitj' of Illinois in partial 
fulfillment of the requirements for the degree of Doctor of Philosophy, June, 1Q09. 



92 



Bulletin No. 145 



[April, 



probably their fertility to its presence since it held in combination, 
phosphorns, nitrog'en, and certain mineral elements. 

Deherain (22) determined the carbon content of soils from 
plots which had received different treatment. He found that the 
soils from the plots which had not been manured had lost over 
50 percent of their carbon. 

Kostytschiff (24) studied the humus obtained from substances 
of known origin and which were converted into humus under con- 
trolled conditions. He learned that even with the albuminous sub- 
stances the carbon was lost more rapidly than the nitrogen, hence 
the ratio of carbon to nitrogen would be narrower in the resulting 
humus than in the original material. 

Berthelot and Andre (31) found that 67.1 percent of the total 
carbon in soils was soluble in dilute alkalis but that over one-half 
of this soluble carbon, or 40 percent of the total carbon, was not 
precipitated from the alkalin solution by the addition of an acid. 

Snyder (37) reported the results obtained by a study of the 
production and analysis of the humus obtained from such sub- 
stances as cow manure, clover, meat scrap, etc., etc., which were 
converted into humus under known conditions. The carbon 
content of the humus varied from 41.95 percent in case of the hu- 
mus produced from cow manure to 57.84 percent in case of the 
humus produced from cane sugar. 

Hess (45) studied the effect of dift'erent systems of treatment 
on the humus of the soil. He found that the ratios of carbon to 
nitrogen and nitrog-en to humus were not materially effected by the 
treatment applied. 

Andre (47) studied the action of potassium hydroxid on the 
carbon compounds of the soil, mould, compost and peat. He de- 
tenuined the insoluble and soluble carbon: the latter he separated 
into two classes; the portion precipitated from alkalin solution by 
the addition of an acid, and the portion remaining in solution. The 
results obtained are expressed in Table i. 



Table 1.— Percentage ok Soluble and Insoluble Carbon and Ratio 
OE Carbon to Nitrogen 







Peat Compost 


Soil 


Mould 




Ratio 
of 

C''N 


Percent 

carbon 

of 

total 


Ratio 

of 

C/N 


Percent 
carbon 

of 
total 


Ratio 
of 

C;N 


Percent 

carbon 

of 

total 


Ratio 
of 

C/N 


Percent 

carbon 

of 

total 


Insoluble portion 


147.6 


24.5 


84.4 


41.0 


82.4 


35.4 


40.4 


41.8 


Sol- 
uble 


a. Precipitated 
bj' acids 


26.9 


44.8 


16.6 


23.0 


27.1 


36.6 


10.8 


18.7 


por- 
tion 


b. Not precipi- 
ta'ed by acids 


17.7 


30.7 


9. 8 


37.0 


16.7 


28.0 


10.1 


39.5 



ipio] Carbon, PiiosriioRus and Nitrogen in Soils 93 

The ratio of carbon to nitrogen in the original material was: 
peat 22.7; compost 15.0; soil 24.7 and mould 12.8. He concluded 
that the more insoluble the compound the wider was the carbon- 
nitrogen ratio. The potassium hydroxid showed a tendency to dis- 
solve the compounds rich in nitrogen. 

Pagnoul (51) found no fixed relation between the carbon and 
nitrog-en of the soil but apparently the carbon, nitrogen, and humus 
varied in the same direction, altho ^irregularly. 

Rimbach (53) concluded that, since the matierc noire was 
readily nitrified it was the direct source of the nitrates of the soil 
and thus the insoluble carbon was of insignificant value. 

Frear and Hess (54) found that lime caused a more rapid loss 
of carbon than of nitrogen in manured land, but the reverse in un- 
manured land. 

Dyer (55) studied the carbon and nitrogen content and the re- 
lationship between carbon and nitrogen in the soil taken from 22 
different plots of tlie Rothamsted experiment fields. These data 
are furnished for each individual 9-inch section to a depth of 90 
inches. 

The carbon and nitrogen contents of the higher depths were 
higher than those of the lower depths and the ratio of carbon to 
nitrogen is wider in the former. At the fifth to sixth depth the 
carbon and nitrogen contents seem to become fixed quantities and 
are apparently those deri\cd from the original matter out of which 
the soil was formed. 

A study of various clays and other material taken from great 
depths seemed to indicate that a nitrogen content of .04 percent 
was indigenous to the subsoil of the Rothamsted station. 

Cameron and Breazeale (61) investigated the three general 
methods for determining the carbon content of the soil : namely, 
the "loss on ignition" method, the humus method and two forms 
of a combustion method. They concluded that the first two meth- 
ods were unreliable : the first, because there was no apparent re- 
lationship existing between the results obtained and the true carbon 
content ; the second, since it makes no pretense of g'iving the total 
carbon in the soil. 

It is interesting to note that they reported that the ammoniacal 
extract contained so much suspended material that it was found 
undesirable to work with, until it was passed through a Chamber- 
land-Pasteur filter, when a perfectly clear solution was obtained. 

Konig {6y) recently studied the influence of hydrogen peroxid 
on the organic matter of the soil. He found that it consisted of 
two parts, one easily oxidized by hydrogen peroxid, the other not 
oxidized by this reagent. 



<H Bulletin No. 145 l^-J /"•'/, 

Hopkins and rdlit {(">><) rep«Tte(l tlic total carbon, nitrogen 
and pliospli(»rns contents of a great nnniber of samples of the soils 
of Illinois This woik r^-, thns, made the basis of calculating the 
relationship of carbon, nitrogen and phosphorus reported in part 
(B) of this thesis. 

2. Nitrogen in Soils 

The nitrogen in soils exists chielly as organic nitrogen with a 
\ery small amount of inorganic nitrogen. The organic nitrogen 
mav exist in some known and probably some unknown forms. 

Aliilder ( 1 ) beliexed the nitrogen, found in the hunuis, to be 
associated \\ ith the organic matter in the form of the ammoniacal 
salts of the \arious organic acids obtained liy him. 

Afiiller (4) thought he detected a tendency for the nitrogen to 
vary inversely as the carbon. 

Detmcr ( () ) believed that the nitrogen formed a dehnite com- 
pound with the ()rganic carbon of the soil since the nitrogeu could 
be liberated onlv with great difficulty and by the use of the most 
drastic chemical agents. 

Simou ( II ) believed that the organic matter of the soil pos- 
sessed the ])ropertv of absorbing the free nitrogen of the at- 
mosphere and (»f con\ertiug it into ammonia which in turn united 
with the organic acids in the form of their ammoniacal salts. Sos- 
tegni ( 10) a little later discussed tlie work of Simon and reported 
a series of experiments to pro\e that Simon's assumption was un- 
tenable. 

Berthelot ( K/), in iSSf>, reported the carbon and nitrogen con- 
ten.ts of calcareons cla\ev soil, originally very deficient in organic 
carlion and nitrogen but which was gradually increasing in carbon 
and nitrogen content owing to the action ot diatoms. 

Berthelot and Andre ( _'(% 74, y^^ 7^) I'der carried on a series 
of experiments for the i)urpose of separating the org'anic nitro- 
genous material into its various compounds. They reported the 
amount of total, nitric, amido and ammoniacal nitrogen present in 
the soil. 

Eggertz (21) differed very materially from Mulder. He con- 
cluded that Alulder's contention, that the nitrogen associated with 
the organic matter of the soil existed onlv as the ammoniacal salts 
(d" the \arious organic aci<ls, was untenable. If the nitrog"en ex- 
isted simph- as the amm()niacal salt of the humic acid, treatment 
with hvdrochloric acid should liberate (/// the nitrogXMi as ammonia, 
wdiich, experimental e\idence showed, was not the case. 

Furthermore artificial humic acid, treated with ammonia, did 
form ammonium humate which, however, was readily decomposed 



IQTO] CaR!!OX, PUUSI'HORII.S AND NiTROGEN IN SoiLS 95 

1)V treatment with a mineral acid; yet, if this artificial hnmic acid 
be heated in a cnrrent of ammonia oas, combination took place and 
the resulting- compound could not be decomjxKsed l)y treatment 
with mineral acids. He, therefore, concluded that the nitrogen 
formed an integi-al part of the humic acid radical. 

Berthelot and Andre (26) studied artificial humic acid pre- 
pared out of sug-ar. This acid formed salts with various bases, 
which were easily decomposed again b}- treatment with an acid, 
except in the case of the aiuuiou'uim salt, the nitrogen of which 
could not be entirelv liberated l)y this treatment. They concluded 
that the nitrog-en in part at least, formed an integral part of the 
humic acid radical. 

Hilgard and Jaft'a (30), in 1892, proi)ounded their well known 
view regarding- the importance of the nitrogen associated with the 
extracted matiere noire. 

Berthelot and Andre (31) regarded the organic matter of the 
soil as of great importance since it prevented the loss of nitrogen 
thru drainage since the nitrogen w^as held in insolu1)le combination 
in the organic matter. 

Fulmer { }fi) determined the humic nitrogen in 53 samples of 
Washington soil and attempted to work out the relationship be- 
tween carbon and nitrogen by means of the formula c= ^-^y 
where c= the percentage of nitrogen in the matiere noire; b= 
the percentage of the total soil nitrogen; a= the percentage of 
humus. By means of this formula the 53 samples of soil were 
separated into three classes; the first class contained 19 samples in 
wdiich the variation in the humic nitrogen calculated l)y means of 
the formula was within one percent of the analytical result; the 
second class contained 10 samples and the variation was from one 
to two percent ; the third class contained 24 samples and the varia- 
tion was anywdiere o\er two percent. These results furnished good 
evidence that no one given relation would hold for all soils. 

Wheeler (48) found that lime or gypsum caused a decrease in 
the amount of humus but that the percentage of humic nitrogen 
was increased. Similar results were obtained l>y Frear and Hess 
(54) on manured land. 

Dojarenko (56) recently studied the '"humic" nitrogen of soils. 
He determined the total, humic, amid, ammoniacal and amido ni- 
trogen in seven samples of Ijlack Russian soils. The results are 
rept^rted in Tal;)le 2. 



96 



Bulletin No. 145 



[At^ril, 



T.\BLE 2.— PkkcEntage of Totai, Humic, Amido, Amid and Am:\ioniacai, 

Nitrogen in Humus 



Percent in dry substance 


Percent of total quantity 
of nitrogen 


No. 


Total 

humic 

nitrog-en 

2.735 

3.38 

2.64 

3.33 

4.58 

3.65 

4.02 


Amido 
nitrogen 

1.34 
1.81 
1.30 
2.34 
1 . 01 
1.26 
1.96 


Amid 
nitrogen 


Ammo- 

niacal 

nitroijen 


Amido 
nitrogen 


Amid 
nitrogen 


Ammo- 

niacal 

nitrogen 


1 

2 

3 
4 

5 
6 

7 


0.31 
0.41 
. 29 
0.32 
0.48 
0.27 
0.22 


0.04 
0.08 
0.02 
0.03 
0.01) 
0.07 
0.03 


49.09 

53.55 
4'».20 
70.27 
22.01 
34.52 
48.75 


11.38 

12.13 

10.99 

9.61 

10. 4() 

7.40 

5.47 


1.46 
2.36 
0.80 
0.90 
1.31 
1.90 
0.78 



'Phis (lid mil account for all of tlic nitroj^'en present and so the 
(lucstion arises in what form docs the remainder exist? 

D'Utra (70) found that the humic nitrog-en showed wide \'ari- 
ations. 

Hilgard (71) reported the average humic nitrogen of 466 
samples of soil from the humid regions as 5.45 percent, while the 
average of 313 samples of soil from the arid section was 15.87 
percent. Later (73) he found that the average humic nitrogen for 
696 samples of humid soil was 5.00 percent, while that of 573 
samples of arid soil was 15.23 percent. It must he remembered, 
however, that the total quantity of nitrogen of the two regions is 
in the inverse order. The total nitrogen of the uplands and low- 
lands of California for example, is o. loi percent and o. loi per- 
cent respectixcly, while the total nitrogen of the ordinary lirown 
silt loam soils of the corn l)elt in Illinois varies from 0.J18 percent 
to 0.337 pci'cent. 

3. rJlOSlMLORlTS IN Soii.s 

The phosphorus of the soil ma\' exist in the inorganic and 
organic condition. The greater part is in the inorganic form with 
an unknown amount in the organic state. The form and amount 
of the organic phosphorus is uncertain, and, indeed it has been 
questioned, especially during recent years, whether or not organic 
phosphorus occurred in the soil to any appreciable extent. 

Milkier ( i), as early as 1844, noted that the organic material 
was not readily freed from phosphorus. 

The work of Thcnard, Schutzenber (5, 6, 7) showed that union 
may take place between various forms of artilicial humus and phos- 
l)hates under certain conditions and indicated that combination may 
possibly take place in the soil between organic carbon and inorganic 
phosphorus. 

Detmer (9) in the preparation of his "pure humic" acid, noted 



/p/o] Carbon, Phosphorus and Nitrogen in Soils 97 

that the material could be freed from phosphorus only with great 
difficulty. 

Grandeau (lo) regarded the phosphorus associated with the 
extracted matierc noire as being of the greatest importance, and, 
was probably in special combination with the org^anic matter. ITe 
regarded it as an index of the fertility of the soil. 

Sinion (ii) believed that he had demonstrated that miion took 
place between organic matter and phosphates. When freshly pre- 
cipitated humic acid was suspended in water and digested with 
calcium phosphate and then filtered, the filtrate showed an excess 
of phosphoric acid : this excess, he concluded must be in union 
with the organic matter in solution. He thought that a double com- 
pound of ammonia and phosphorus existed in the soil. 

Schultz (12) showed that the addition of humus to "Basalt- 
boden" increased the absorption al)ility of the soil for phosphates. 

Eichhorn (13) repeated some of Simon's work and concluded 
that organic cohibination did not take place as indicated by Simon 
but that the humus had decomposed the tri-calcium phosphate with 
the fomiation of acid phosphate. 

Pitsch (14) determined the solubility of the various mineral 
phosphates, including iron and aluminium phosphates, in a solu- 
tion of auiuwn'unn luiniatc itself. He concluded, that, since this 
solution exerted a solvent action on mineral phosphates, the am- 
monia extract of the soil contained phosphorus, other than that 
originally associated with the organic matter in the soil and prol)- 
ably part, at least, of the ammonia soluble phosphorus was derived 
from the iron and aluminium phosphates. 

M. P. DeGasparin (15) found in calcareous clav soil five per- 
cent of the total phosphorus in organic combination. He noted, 
furthermore, that the mosses and lichens contained from 5 to 6 
times as much phosphorus as the rocks on which they grew ; the 
soil formed therefore, from tlie debris of these plants should be 
relatively richer in phosphorus and should have a part of its phos- 
phorus in combination with carbon in the organic material. 

Eggertz (21) found that the ammoniacal extract of the soil, 
when treated with an acid, formed a precipitate of organic matter 
which always contained phosphorus. He concluded, therefore, that 
part of the phosphorus of the soil w^as united to the carbon in or- 
ganic combination. 

Later, Eggertz and Nilson demonstrated that the amount of 
phosphorus soluble in dilute mineral acids showed a marked in- 
crease after ignition of the soil. Ignition rendered 10 times as 
much phosphorus soluble in 2 percent hydrochloric acid. They 
attributed this to the destruction of the organic matter which had 
held the phosphorus in combination which would not vield up its 
phosphorus to acids. 



93 Bulletin No. 145 [AprU, 

Van Bemmelen (23) believed that the ir<ni, calcium, silica, 
phosphoric acid, etc., found in the ash of the iiiaticrc noire by Eg"- 
f>-ei"tz, were not originally chemically combined to carbon in the 
ori^-anic matter of the soil but were al)s<)rbed by the precipitated 
oelatiuous iiuilicrc Jioirc. According- to X'an r.emmelen the i)h()s- 
phorus existed in the soil ])rincipally as calcium ])h(>sphate with a 
verv small quantity occurriug in the alj-orhcd state in the torm of 
a colloid al 01 I'liiiiiatc-Silicot-Koiiit'h'.v. 

Two questions seemed to be of parauiount impurtance to Wik- 
luud (JS) regardini;- the work of Kg-o-ertz : hrst, was the amount 
of the ammonia-soluble phosphorus obtained from different soils 
constant? v^econd, did the |)hosphorus exist in the mullk()rpers 
(Iiiaticrc noire of Grandeau ) in chemical com1)ination with carl)on, 
or simply as absorl>ed phosphorus? lie concluded that there was 
a tendency for the ammonia-soluble phosphorus to be constant in 
different soils. lie showed, further, that one digestion with 12 
percent hydrochloric acid did not completely remove all of the 
acid soluble phosphorus, ])ut a second and e\en a third digestion 
still remo\-ed some phospliorus. Xow, he reasoned, if the phos- 
phorus removed by the second and third digestion was simply ex- 
tracted fr(_»m the absorl>ed ])liosphorus, extraction of the soil with 
ammonia after the iirsl dig"estion with hydrochloric acid, should 
yield a solution of iiiaticrc noire containing a higiier phosphorus 
content than when the soil was conq)letely extracted with the hy- 
drochloric acid. Such, however, was not the case, therefore, the 
phos])horus did not exist as absorbed phosphorus and must be in 
coml)ination with carbon in the organic matter. 

Snyder (34) noted that some phosph()rus, iron, etc., were ex- 
tracted' with the iiialicrc noire lint he did \vA seem to think at this 
time thai lliere was an\- e\idence of coml)ination with carbon. 
About the same time he ol)served the rapid loss of phospliorus as- 
sociated with the humus in continuous cnhi\ated soil. 

According to P.erthelot and Andre ( .7) phosphorus may be 
found in the soil (a) in inorganic or mineral ])hosphates, (b) in 
organic ethers and (c) in oiganic or mineral com[)ounds not read- 
ily decomposed. 

Schmoeger ( J() ) re\ iewed the rival claims of Eggertz and Nil- 
son, and Wiklund on the one hand, and Van Bemmelen on the 
other, regarding the phenomenon of ignition rendering the phos- 
])horus of peaty soil more readily soluble in acids. 

It seemed possible to Schmoeger that the soil might possess 
such a tenacious absorbent power (or jjlmspliorus that it would not 
vield u]) its ])h. )S])horus to acid treatment before ignition. But he 
deduced experimental exidence to show that such was not the case. 



ipio] Carbon, Phosphort's and Nitrogen in Soils 99 

Digestion of the soil itself and also the extracted inatlerc noire 
with a solntion of potassinni h_\drogen phosphate failed to add any 
phosphorus which was not again recovered hy treatment with 
liydrochloric acid. This was conclusive evidence to Schmoeger 
that the phosphorus did not exist as absorbed phosphoiiis and must, 
therefore, exist in organic combination. Two possibilities sug- 
gested themselves to Schmoeger : first, the phosphorus existed in 
the form of lecithin; second, it existed as nuclein. Lecithin was 
found to be present only in traces. The characteristic property of 
nuclein to "split-off"' its phosphorus in the form of phosphoric 
acid, when heated, under pressure in the presence of water, to* a 
temperature of 150°-! 60° was utilized by Schmoeger. The soil 
under examination, treated in this way, yielded as much soluble 
phosphorus as did the ignited soil. This experimental evidence 
led him to conclude that nuclein or some closely allied bodies were 
present in the soil. 

Later Schmoeger (39) cc^nfirmed his previous work and pro- 
duced additional evidence in fav(M- of his view that nuclein or simi- 
lar bodies existed in the S()il. Tal)le 3 shows some of the results 
obtained. 

Table 3. — PercenTagk of Sui^kuric Acid and Phosphorus Soluble in 

Dilute Acid 



Percent 




Soil in original state 0.122 0.043 

Evaporated soil 290 0.083 

Ignited soil 0.939 0.095 



Since sulfur is regarded bv many authors as being a constitu- 
ent of plant nuclein, the increased solubility of this substance to- 
gether with the phosphorus when the soil was treated as indicated 
above, was reg'arded as evidence in favor of his assumption. 

In a later article (40) he .showed, by similar treatment, that 
analogous bodies existed in the moor grass out of which the moor 
soil was formed. Tliis was regarded as additional exidence in favor 
of his view. 

Tacke (33) observed that the drying out of soil rendered the 
phosphorus available. There were three possible explanations sug- 
gested to him: first, the phosphorus existed in the soil in organic 
coml)ination which was destroyed l>v the process of drying; second, 
it existed in the soil in the. colloidal form as suggested by Van Bem- 
melen ; third, the drying out of the soil gave rise to substances of 
a strong acid nature which acted upon the insoluble phosphorus 
compounds rendering the phosphorus soluble. 



100 Bulletin No. 145 [April, 

In a later article (42) he showed that very little water soluble 
phosphorous existed in the soil under consideration, but that dry- 
ing at 70°-8o° rendered o\'er 50 percent of the total phosphorus 
soluble in water. 

Snyder (36) repi^rted results of a confirmative nature regard- 
ing the phosphorus associated with the humus in virgin and cul- 
tivated soils. 

Later he (37,41) studied the product obtained by the conver- 
sion of known substances, under known condition, into humus. 
The ash of the uiaticrc noire obtained from this material contained 
phosphorus, among other substances, and according to Snyder : 
"There is every indication that these elements are in organic com- 
bination with the carbon, hydrogen and oxygen of the humus." 
As regards the question whether or not the humus united with the 
inorganic phosphorus of the soil, he concluded that his experi- 
mental evidence showed that such union did take place. 

Nannes (49) found that a well decomposed peat soil contained 
0.166 percent pliosphorus. He found that 0.057 percent of phos- 
phorus was extracted with the uiaticrc noire. When the ammonia- 
cal solution of the uiaticrc noire was treated with hydrochloric acid, 
0.039 percent of the phosphorus was found in the organic precipi- 
tate. He also attempted to isolate a definite organic phosphorus 
compound and he l)elieved that he detected the presence of lecithin 
and chlorophyllan. 

Ladd (43) found in a study of eight samples of ditYerent soil 
that an average of 41 percent of the phosphorus was associated 
with the extracted niaticre noire; the variation, however, was 
from 10 percent to 90 percent. 

In a later article (44) he showed that as the humus of the soil 
increased the phosphorus associated with the extracted uiaticrc 
noire also increased. From the fact that the organic precipitate, 
fonned by neutralizing the ammoniacal extract, contained the phos- 
phorus he concluded that it existed in the soil in organic combina- 
tion, but just what the relationship was not clear. 

Emmerling (52) believed that there were four forms of phos- 
phorus in the soil, one of which was phosphorus in organic com- 
bination. 

Rimbach (53) found 6.15 percent P2 O5 in the ash of the 
maticrc noire which was precipitated from the ammoniacal solu- 
tion by the addition of gypsum and magnesium sulfate. 

Nagaoka (57) found that ignition of the soil for fifteen min- 
utes at a faint red heat materially increased the availability of the 
l)hosphorus. He attributed this action to the destruction of the 
liuniopliosphates. 



I9I0] 



Carbon, Phosphorus and Nitrogkn in Soils 



101 



Aso (58) continued, in a i;-encral way, the rcsnlts obtained by 
Schmoeger. He also found 0.049 percent of lecithin in the soil. 
He drew the following- conclusions: 

1. Phosphorus existed in the soil as inorganic and organic 
compounds. 

2. The organic phosphorus material was principally nuclein 
with a very small part of lecithin. 

3. Ignition rendered the phosphorus in organic coml)ination 
available. 

Hart well and Kellogg (60) found that an axerage of one-half 
of the phosphorus was associated with the organic matter in the 
soil taken from four plots which had received different treatment. 

Dumont (62) studied a complete manure, the composition of 
wdiich was as follows: soluble matter (in dilute alkali) 50.4 per- 
cent; insoluble matter 49.6 percent; total nitrogen [.6 percent; 
total phosphorus 1.27 percent. 

The solul)le portion contained 35 percent nf the nitrogen and 
46 percent of the phos[)horus. In order to obtain data u[)on the 
state of combinatiitn of the phosphorus, the amnioniacd solution 
of matiere noire was treated with various reagents with~the result 
(recalculated to the element basis) shown in Table 4. 



Table 4. — Distribution of Phosphorus When Matiere Noire is 
Precipitated 



Precipitatiiijir aj^etil 



Citric acid 

Hydrochloric acid. 

Ferric chlorid 

Aluminium sulfate 
Calcium chlorid... 



Phosphorus 


In precipitate 


In filtrate 


0.383 
0.386 
0.532 
0.566 
0.5S4 


203 
0.199 
0.053 
0.019 
0.0009 



These results furnished conclusive proof to Diimont that a part 
of the phosphorus of the soil was in organic combination. 

Later (64) he obtained better cultural results from application 
of humic phosphatic manures than from mineral phosphatic ma- 
nures and better even than from barnyard manure, which he at- 
tributed to the phosphorus in organic combination. 

In a still later article (65) he said that the organic phosphorus 
was derived from two .sources: first, from the nuclein and lecithin 
of the decaving vegetable and animal debris; .second from the 
union of the humus with the water soluble phosphates of the soil. 

Evidence of the latter contention was ol)tained by precipitating 
the matiere noire in the presence of potassium hydrogen phosphate 
by different reagents as indicated in Table 5. 



102 



Bulletin No. 145 



[Atfii 



Table 5. — Amount ok PhOvSphorus in Pkecipitatrd Humus and Filtrate 





Series A 
Phosphorus in- 
troduced=.087 


Series B 
Phosphorus in- 
troduced = .218 


Series C 
Phosphorus in- 
troduced= .437 


Precipitatiiii; 
agent 


Phos- 
phorus 

in 
humus 


Phos- 
phorus 

in 
tiltrate 


Phos- 
phorus 

in 
humus 


Phos- 
phorus 

in 
filtrate 


Phos- 
phorus 

in 
humus 


Phos- 
phorus 

in 
filtrate 


Acetic acid 

Citric acid 

Hydrochloric acid 
Sulfuric acid 


0.056 
0.054 
0.0.57 
0.057 


0.031 
0.033 
0.030 
0.O30 


0.057 
0.055 
0.05*» 
. 061 


0.160 
0.163 
0.158 
0.156 


0.058 
0.054 
0.059 
0.062 


0.374 
0.381 
0.378 
0.372 



Altho the amount of dipotassiuni phosphate added to the 
sohition had increased, tlie amount of phosphorus absorbed by the 
liumus was practically constant, due to the fonnation of detinite 
"composes phospho-humicjue." 

KcMiig- (67) found that hydroi^'en peroxid oxidized from 40 
l)ercent to 70 percent of the humus present in the soil and that 
much more of the phosphorus was soluljle in pure and carbonated 
water aftei^ oxidation than before, due, he believed, to the destruc- 
tion of the organic phosphorus compounds. 

Fraps (69), quite recently, made a study of the phosphorus 
extracted from the soil by 4 percent ammonia in the usual deter- 
mination of humus. Tie conhrmcd Pitsch's results regarding- the 
possibility of some of the ammonia-S(^lublc pliosphorus being of 
inorg^anic orig'in. He separates tlie ammonia-soluble phosphorus 
into three classes as follows: 

1. The phosphorus associated with the clay held in suspension 
in the liquid. 

2. The phosphorus precipitated with the organic matter when 
the sr)]ution was neutralized with an acid. 

,V The phosphorus which remained in solution after the pre- 
cipitation of the organic matter. 

With the soils under consideration he found that i ^9 of 
the ammonia-soluble phosphorus was in the lirst class, 1/3 was in 
the second class and 5/0 was in the third class. 

The phosphorus found in the first class was assumed to be as- 
sociated with tlie clay particles as iron and aluminium phosphates. 
He concluded that the phosphorus precipitated with the organic 
matter from the ammonical solution by the addition of acids was 
in organic combination. The phosphorus remaining in the mother 
liquor was assumed to be derived from the iron and aluminium 
phosphates of the soil. 

Mooers and Hampton (y-) recently proposed a method for 
obviating the error introduced in I he humus determinations by the 



ipio] Carbon, Piiospiiorus and Nitrogkn in Soils 103 

suspended clay. They claimed that filtration throug-h the Cham- 
berlain-Pasteur iilter, as suggested by Cameron, introduced a 
serious error inasmuch as the filter absorbed some organic matter. 
They proposed an evaporation method : by evaporation of the 
ammoniacal extract to dnaiess re-dissolving in ammonia and filtra- 
tion, several times, a perfectly clear solution was obtained. Deter- 
mination of the humus in this filtrate gave very concordant results. 
Hopkins and Pettit (68) found that in certain soils the mineral 
composition had a tendency to be constant in the surface, sub- 
surface, and subsoil. This was indicated by the unifonn potassium 
content of the surface, subsurface, and subsoil and by the fact that 
dift'erent samples of surface soil of the same type showed a wide 
variation in the phosphorus content but that this variation largely 
disappeared in the subsoil. The potassium exists in the soil in the 
inorganic form, the nitrogen exists chiefly in the organic form while 
the phosphorus may exist in the inorganic and organic state. They 
suggested, therefore, a method for calculating the phosphorus in 
the organic state in the surface soil. The difference in amount of 
nitrogen in the surface soil and subsoil, and the difTerence in the 
amount of phosphorus in the surface soil and subsoil gave appar- 
ently the amount of nitrogen and phosphorus associated together 
in organic combination. By means of this ratio and the total 
amount of nitrogen in the surface soil tlie total amount of organic 
phosphorus present in the surface soil could be calculated. 

4. Carbon and Nitrogen Content of Fundamental Rocks 

The fundamental rocks out of which soils have been formed 
contain an apprecial)le amount of carbon and nitrogen which is in- 
digenous to them. 

Dellese (3) discovered that mineral matter, crystalline, sedi- 
mentary and eruptive contained carbon associated with nitrogen. 
This mineral matter, which was formed under similar conditions 
of temperature, pressure, etc., had a tendency to contain a constant 
amount of carbon and nitrogen. 

The work of Lawes and Gilbert (16), Dyer (55) and Hall and 
Miller (66) on the clays and other fundamental rock material 
taken from various great depths indicated that an appreciable 
amount of carbon and nitrog'en was indigenous to the underlying 
soil material. 



IQIO] 



Carbon, Phosphorus and Nitrogen in Soils 



105 



(B) EXPERIMENTAL PART 

The starting point of snch an investigation consists of a con- 
sideration from a mathematical point of view of the existing- data 
reg'arding tlie relationships of carbon, phosphorus and nitrogen of 
the soil. 

I. Mathematical 

(a) INEI.UKNCK OE AGE ITPON THE NlTROf.EN-CARBON RATTO 

From the data availaljle in the literature it is possil)le to deter- 
mine within certain limits the intlnence of age upon the nitrogen- 
carbon ratio in soils. From the average results of a number of 
nitrogen determinations (68) and the carbon content obtained by 
calculation fr(_»m the proximate analysis, it is possible to determine 
the approximate nitrogen-carbon ratio in the more common humus 
producing materials. The results obtained in this way will be 
foiuid in Table 6. The materials naturally fall into tv/o groups: 
in the first gi'oup the ratio varies from i :^2.2 for corn stover to 
I 184. 1 for wheat straw; in the second group the \ariation is from 
I nf)./ for alfalfa hay to i :35.4 for timothy hay. 

Table 6. — Approximate Nitrogkn-Carbon Ratio in the More Common 
Humus Producing Materials 



Kind of material 



Corn stover. 
Oat straw. . . 
Wheat straw 

Timothy hav, 
Clover hay. . . 
Cowpeahay. , 
Alfalfa ha3'. . 

Albumin ... 

Zein 

Nuclein .... 



Carbon tol 
of nitrogen 



52.2 
67,8 
84.1 



35.4 
21.3 
19.5 
16.7 



32 
3.4 



In Table 6 will also be found the nitrogen-carbon ratio in some 
of the compounds which might be expected to be found in humus. 
The ratio is very narrow and does not vary much from i :3. 

The next step in the study in the influence of age upon the 
nitrogen-carbon ratio would l)e to determine the ratio in as fresh 
humus as possible from known materials. Snyder (35) in his 
studv of the production of humus from known materials placed a 
weighed quantity of the material together with a weighed quantity 



106 



Bulletin No. 145 



[April, 



of soil having a low humus content in a bux and set aside for one 
vear. At the end of the experiment the humus was extracted and 
the carl)on and nitrogen determined in the inuticrc noire. At first 
thought this would appear to furnish the desired information, but 
unfortunately no check was run with the untreated soil, so no cor- 
rection can be made for the carbon and nitrogen which may have 
been converted into humus from the unhumified material of the 
soil. This i^ evidently not a cpiantity which can be ignored since 
the humus C()ntent of the original soil is .06 percent while the total 
nitrog'en of the soil is .02 percent showing that considerable un- 
humified organic matter was present, otherwise the humic nitrogen 
would be 33.33 percent while it has been shown (71) that the 
luimic nitrogen would more probal)ly be nearer 5 percent. In ad- 
dition, the fact that the humus obtained from sugar contains some 
nitrogen is evidence that some of the unhumified organic matter of 
the soil has been converted into humus, since sugar does not con- 
tain nitrogen. The results, however, will be found in Table 7. In 

Tabi,e 7.— Minnesota Soii< Studies: Humus Pkoduction From Known 

Materiai^s 





Percent 


Ratio of 


Material used 


Humus 


Carbon 
in humus 


Nitrogen 
in humus 


carbon to 1 
of nitrogen 


Original soil , 


0.06 
0.58 
0.37 
0.31 
0.46 
0.47 


41.«t5 
54 . 22 
48.77 
54 . 30 
51.02 


? 
6.16 

8.24 

10.96 

2.50 

5.02 


? 


Cow manure 

Clover 


6.8 
6.6 




4.5 


Oat straw 

Flour .... 


21.7 
10.2 






Saw dust 

Sugar .... 


0.59 
0.32 


49.28 
57.84 


0.32 
0.08 


153.8 
741.0 



the first five substances the variation is from i :2i.7 for oat straw 
to I :4.5 for meat scraps. 

The large number of carbon and nitrogen determinations made 
in the soils of Illinois (68) rendered it possible to determine the 
nitrog'en-carbon ratio, not only for the surface soil, Ijut also for 
the subsurface and subsoil. The average of 19 determinations for 
the soil type, gray silt loam on tight clay, gave the ratios i :io.4, 
1 :8.8, and i 17. 6 for the surface, sul)surface, and subsoil re- 
spectively. The ordinary brown silt loam soils as an average of 
68 determinations gave a nitrogen-carbon ratio of 1:12.1, 1:11.5 
and 1 :8.9 for the surface, subsurface, and subsoil respectively. The 
1)lack cla)' loam soils as an average of 25 determinations g^ave 
1 :ii.7, I :ii.<) and 1 :f) respectively in the surface, subsurface, and 
subsoil, 'i'hc peat soil as the average result of 5 determinations 
gave I :ii.8 and t :i2.9 for the siu^face and subsoil respectively. 



ipio] 



Carbon, Phosphorus and Nitrogen in Soils 



107 



Tabi,e 8 —Ratios ok Carbon and Nitrogen in Ii^i^inois Soii^s 



Soil 
type 
No. 


Soil types 


No. of 
analysis on 

which 

calculations 

are based 


Carbon to 1 of nitrogen 


Surface 


Sub- 
surface 


Subsoil 


330 
426 
526 
626 
726 
1126 
1026 


Gray silt loam on 

tight clay 

Brown silt loam 

Brown silt loam 

Brown silt loam 

Brown silt loam 

Brown silt loam 

Brown silt loam 


19 
11 
8 
6 
4 
30 
9 


10.4 
12.5 
13.2 
11.4 
11.9 
11.9 
12.0 


8.8 
11.7 
12.9 
10.5 
11.1 
11.5 
11.5 


7.6 
9.6 
8.7 
8.7 
8.8 
8.6 
9.3 


Averages 


68 


12.1 


11.5 


8.9 


420 

520 

1120 

1220 


Black clay loam 

Black clay loam 

Black clay loam 

Black clay loam. . . . 


7 

5 

11 

2 


12.2 
12.4 
11.1 
11.2 


12.2 

12.2 
ll!l 
12.2 


8.9 
11.4 

8.3 
7.4 


Averag-es 


25 


11,7 


11.9 


9.0 


1401 Deep peat 


5 


11.8 


12.9 


12.9 



The Rothamsted work furnished information regarding the 
nitrogen-carbon ratio of the soil in nine inch sections to a depth of 
90 inches. These resnUs will be found in Tables 9 and 10. The 
ratio for the Broadbalk wheat fields varies from i 19.5 to 4.8 for 
the surface and ninth 9 inches respectively. After the fifth 9 inches 
there is very little change in the ratio. In the Hoosfield barley 
soils the ratio varies from i :io.6 to i :8.8 for the surface and sub- 
soil respectively. 

Tabi,e 9.— Broadbalk Wheat Soils: Ratio of Carbon to Nitrogen 



Depth 

First 9 inches (all plats) 

Second 9 inches 

Third 9 inches 

Fourth 9 inches 

Fifth 9 inches 

Sixth 9 inches 

Seventh 9 inches 

Eighth 9 inches 

Ninth 9 inches 

Tenth 9 inches 



Percent 



Carbon 



1.155 
.640 
.492 
.339 
.279 
.256 
.248 
.215 
.189 
.188 



Total ni. 
trogen 



.1222 
.0784 
.0666 
.0511 
.0472 
.0430 
.0420 
.0396 
.0391 
.0375 



Carbon to 1 
of nitrogen 



9.5 
8.2 
7.4 
6.6 
5.9 
5.9 
5.9 
5.4 
48 
50 



Table 10 — Hoosfield Barley Soils: Ratio of Carbon to Nitrogen 



Depth 


Carbon to 1 
of nitrogen 


First 9 inches 


10 6 


Second 9 inches 


8^8 


Third 9 inches 


8 8 







108 



Bulletin No. 145 



[April, 



Hall and Miller (66) reported the carbon and nitrogen con- 
tent, and ratio of carbon to nitrogen in samjiles of \-aric)ns ma- 
terials taken from such great de[)ths as to preclude all possibility 
of weathering. Since the nitrog'en was always found to be associ- 
ated with carbon it w^as regarded as being of organic origin and 
as being deri\ed in part from the organic matter present in the 
clav at tlie time of its deposit. These results are shown in Table ii. 

TabIvE 11. — Carbon and Nitrogen in UnweaThered Rocks 



No. of 
soil 



3 

4 

5 

(» 

7 

8 

9 

10 

11 

12 

13 

14 



Formation 



Lower Bag-shot Sand, Weybridg-e. . 
Upper Greensdiid, Farnham, Surre}' 
Folkestone Beds, Brabourne, Kent. 

Lower Greensaud, Sevenoal^s 

London Clay, London 

Gault Clay, Nackholt, Kent 

Weald Clay, Pluckley. Kent 

Caiboniferous Shale, Barnsley... 

Lower Gault, Dover 

Oxford Clay, Dover 

Kimmeridge Oay, W^elton Lines. . . 

Kimmeridge Cla3', Dover 

Lower Lias, Micketon, Glos 

Clay with Flints, Harpenden 



Ueptb at 
whichsani- 
ple was ta- 
ken, ft. 



Percent 



Organic 
carbon 



18 20 

30 

20 

30 

130 

18 

30 

1236 

280—400 

920 

246 

570 

700 

10 



0.02 

0.032 

019 

0.076 

391 

427 

135 

1.938 

0.172 

0.548 

2.139 

0.387 

1.120 

577 



Nitrogen 



.00384 

.00718 

.00453 

.00881 

.041 

.0415 

.0647 

.137 

.0325 

.0528 

.107 

.0455 

.0803 

.0294 



Ratio 



5.4 

4.5 

4.2 

8.7 

9.5 

10.3 

2.1 

14.1 

5.3 

10.4 

20.0 

8.5 

13.9 

19.6 



NOTES 

1. A grey coarse sand. 

2. Pale g:rey tine sandy rock. 

3. Coarse yellowish sand. 

4. Fine yellowish sand. 

5. Solid grey clay. 

(). Solid dark green clay. 

7. Close grey and red mottled clay. 

8. Hard gre^' shale. 

9. 10, 12. Hard grey clays from the coal pit shafts at Dover. 
11. Hard grey clay. 

13. Hard grey clay. 

14. Reddish sandy brick earth. 

It will be seen from a study of the abo\e tal)les that 
normal conditions the nitrogen-carbon ratio ot the soil has 
ency to become narrower as the age of the organic mater 
creases. 'J'he i-atio, howe\er, ne\er becomes narrower ( 
ei|ual to the ratio of the more common proteins contained 
humus i)roducinu' materials. 



under 
a tend- 
ial in- 
)r ever 

in the 



(b) CARHON, NITR()('.i;m ANI:) PlIoSl'llROtTS IX TIJJNOIS SOII.S 

IJefore discussing the ])hosphorus-carbon and ])h(^sj)horus- 
nitrogen ratios in the soil it seemed desirable to determine as closely 
as possible these ratios in fresh material out of which humus mig^ht 
be formed. 



IQIO] 



Carbon, Phosphorus and Nitrogen in Soils 



109 



Table 12. — Approximate Carbon-Phosphorus and Nitrogen-Phosphorus 
Ratios in the More Common Humus Producing Materials 



Kind of material 


Carbon to 1 
of phospho- 
rus. 


Nitrog-en to 
1 of phos- 
phorus 


Corn stover 


417 


8.0 


Oat straw 

Wheat straw 


420 
525 


6.2 

6.2 


Timothy hay 

Clover hay 

Cow pea hay 


283 
171 
181 
186 


8.0 
8.0 
9.3 


Alfalfa hay 


11.1 






Nuclein 


3.7 


1.4 







The ratios in the more common humus producini^- materials 
calculated from the average of a numl)er of analysis for nitrogen 
and phosphorus (68), will l)e found in Ta])le u. In the coarser 
material the phosphorus-carbon ratio varies from 1:417 to 1:525: 
the phosphorus-nitrog'en ratio is more constant being i :6.2 and 1 :8. 
In the hays, the phosphorus-carbon ratio varies from i :i86 to i :283 
while again the phosphorus-nitrogen ratio is more constant, the 
variation being i :ii.i to i :8. In nuclein tlie ratios are i 13.7 and 
I :i.4 respectively. 

In Table 13 will be found the phosphorus-carbon and phos- 
phorus-nitrog'en ratios obtained by calculation from the Minnesota 
Soil Studies. The phosphorus determinations which were reported 
as phosphoric anhydrid were first recalculated to the element basis. 
Both ratios, it will l)e observed, are \er)- narrow. 

In Table 14 will be found the pho.sphorus-carbon and phos- 
phorus-nitrogen ratios in Illinois soils calculated from the data re- 
ported by Hopkins and Pettit (68). The average of 7 calculations 
of the gray silt loam on tigiit clay ga\e the phosphorus-carbon and 
phosphorus-nitrogen ratios as i :42.6 and i :i3.8 respectively. 



Table 13.— Minnesota Soil Studies: Carbon-Phosphorus and Nitrogen- 
Phosphorus Ratios 



Kind of material 

Original soil 

Cow manure 

Clover 

Meat scraps 

Oat straw 

Flour 

Sawdust 

Suffar 



Carbon to 11 Nitrogen to 
of phospho-j 1 of phos- 
rus. phorus 



9.8 
11.2 

9.7 
38.2 
22.0 
37.0 
42.4 



1.4 
1.7 



0.24 
0.06 



110 



Bulletin No. 145 



[April, 



Table 14. — Illinois Soils: Okc.anic Phosphokus; Ratios of Carbon to 

Phosphokus, Nitkogkn to Phosphorus and Carbon to Nitrogen, 

Factors kor Calculating the Organic Phosphorus. 





Number of aii- 

alysisoii which 

calculations 

are based 


Organic phos- 
phorus as per- 
cent of total 
phosphorus 


Ration of 


Factors for 
calculating the 
organic phos- 
phorus from 
the organic 
carbon 


Soil 
type 
No. 


Carbon to 1 
of organic 
phosphorus 


Nitrogen to 
1 of organic 
pliosphorus 


330 7 


24.4 


142. 


13.8 


0.007012 


426 
526 
626 
726 
1126 
1026 


9 
8 
5 
4 
24 
9 


34.4 
29.5 
13.9 
38.1 
40.9 
44.9 


132. 
185. 
298. 
133. 
116. 
125. 


10.6 
14.0 
25.1 
10.5 
9.9 
10.9 


0.007570 
0.005393 
0.003348 
0.007491 
0.008583 
0.007988 


Average 59 


33.5 


165. 


13.5 


0.006053 


420 

.520 

1120 

1220 


7 

5 

11 

2 


36.0 
33.8 
46.2 
32.4 


134. 

260. 

90. 

169. 


10.3 

12.0 

8.3 

15.2 


0.007441 
0.00383() 
0.005907 
0.002956 


Average 25 


37.1 


163. 


11.4 


0.006113 


1401 
1401 


4 
(b) 5 


100.0 
100.0 


230. 
338. 


19.6 

26.5 


0.004311 
O.00295<) 



(b) Subsoil (7" 40") 

The ordinary brown silt loam soils, as an average of 59 deter- 
minations, g-ave the ratios of i 1165.2 and i :i3.5 respectively. The 
lilack clay loam soils, as an average of 25 calculations, gave the 
ratios of i 1163 and i :ii.4 respectively. The ratios in the surface 
peaty soil, assuming all the phosphorus to be in the organic state, 
are i 1230 and 1 :i(;.6. The ratios in the subsoil of the peaty soil 
are somewhat wider, l>eing i 1338 and i :26.5 respectively. 

(c) FACTORS I'OR CALCULATING ORGANIC PHOSPHORUS 

By means of the carbon-phosphorus ratios established as in- 
dicated aboxe, it is possible to develop factors for calculating the 
amount of the org-anic phosphorus in the surface soil from the 
total organic carbon. For example the carbon-phosphorus ratio, 
I :i63, in the black clay loam soils means that for every part of 
organic phosphorus there are 163 parts of carbon or for each part 
of organic carbon there are 0.0061 13 parts of organic phosphorus. 
Hence by multiplying the amount of organic carbon by the latter 
number the amount of organic jihosphorus may jje obtained. 

The factors as developed will be found in the last column of 
Table 14. It is hoped that they will be of value in drawing broad 
general conclusions regarding organic phosphorus of the soil from 
a numl>er of analyses. The variations in the various samples con- 
sidered in any single type are too great to permit the utilization of 
the factors in isolated cases. 



JQIO] 



Carbon, PHOsriioRUs and Nitrogen in Soils 



111 



• It will be observed that from 1/4 to 2/5 of the total phos- 
])horiis of the several soil types considered is in organic combina- 
tion. These results indicate that a larg'er amount of phosphorus 
is in org-anic coniliination than the work of some American inves- 
tigators would lead us to believe. 

2. Chemical 

(a) ANATA'TICAI, RKSUT/rs OF SOIL, FROM TTJJNOTS SOUTH F.XPFRI- 

MFNTAL FARM 

A sample of soil iov a study of the (Organic phosphorus, by the 
available methods for the determination of the organic phosphorus 
of the soil, was obtained from the Illinois South Experimental 
Farm. This soil is the ordinary brown silt loam soil of the corn 
belt. 

The total potassium, carbon, nitrogen, and phosphorus in the 
surface and subsoil were determined l)y the methods adopted by 
the Illinois Experiment Station. The results, expressed as pounds 
per two million pounds of dry soil, will be found in Table 15. The 
average potassium content of 36,700 pounds, and 37,070 pounds in 
the surface and subsoil indicate a constant mineral composition, 
hence the calculation method may be safely applied for the deter- 
mination of the org'anic phosphorus. The amount of organic phos- 
phorus, the various ratios and the developed factor will be found 
in Table 16. It will be seen that 46 percent of the total phosphorus 
in this soil is in organic combination. 



Tabi,E 15. — Anaia'Tical Rksults of Soii. from Ii,i^inois South Experi- 
mental Farm: RESut,TS Expressed as Pounds in Two Mihion 
Pounds of Dry Soii. 



Soil No. 


Soil 
stratum 


Potassium 


Carbon 


Nitrogen 


Phos- 
phorus* 


lA 
IB 

Average 

3A 
3B 

Average 


Surface 
Surface 

Surface 

Subsoil 
Subsoil 

Subsoil 


36280 
37120 

36700 

36600 
37540 

37070 


41800 

42180 

41.90 


3760 
3844 

3802 

1735 
1680 

1708 


938 
901 

919* 

702 
670 

686 



*I,ater inspection of tlie strip of land from which this sample was taken led to the conclu 
sion that it may have been modified by a previous disturbance of the soil in putting- in tile 
drainag-e; and aconiposite sample was subsequently collected at points a short distance from 
the tile drain which showed 'J85 pounds of phosphorus instead of 'n'> pounds. The possible 
influence of this difference should be kept in mind. Thus the percent of total phosphorus in 
organic form would be reduced from 4t) percent to 43 percent.— C. G. Hopkins. 



112 



Bulletin No. 145 



[April, 



Table 16. — Organic Phosphorus: Ratios of Carbon to Organic Phos- 
phorus, Nitrogen to 1 Organic Phosphorus, Carbon to Nitrogen 
IN Surface Soil 



Pounds of 

organic 

phosphorus 


Organic 

phosphorus 

as percent 

of total 
phosphorus 


Ratios of 


Factor for 
calculating 
the organic 
phosphorus 
from organic 
carbon 


in two 

million 

pounds of 

soil 


Nitrogen 
to 1 organic 
phosphorus 


Carbon to 
1 nitrogen 


Carbon to 

1 organic 

phosphorus 


423 


46.0 


9.0 


11.1 


99.2 


0.01008 



(1)) I'lK^Sl'IIORUS ASSOCIATKl) WITH TllK MATIERK NOIRK 

Of the two a\ail;i1)lc melliock for (leterniining the organic 
])hosphoriis, the one, tlie determination of the phosphorus associ- 
ated with the iiialirrr )ioirc extracted from the soil Iw 4 percent 
ammonia, has given rise to some confusion. Grandeau (10) re- 
garded the phosphorus extracted with the iiiatii-rc noire as being 
probably in organic combination. Kg"gertz (^i), Nilson (79), 
Wiklund (J5), Dnniont (O5), Ladd (43) and Snyder (41) also 
regarded it as organic in form. Pitsch (14) and Van Bemmeleii 
(23) took the opposite view. I'itsch thought that part of the ex- 
tracted phosphorus may ha\e been derived from the inorg'anic 
phosphates of the soil. \'an Bemmelen regarded the phosphorus 
precipitated with the iiiaiicrc noire as absorbed phosphorus. Quite 
recently, Fraps {(nj) concluded that onl_\- 1/3 of the phosphorus ex- 
tracted Ijy ammonia was in organic conil)ination, wdiile still later 
vStoddart (80) concluded that only 15 of the extracted phosphorus 
was in organic combination. As a result of this contiicting evi- 
dence there is considerable C(»ntusion regarding the nature of the 
phosphorus extracted by ammonia. One cause of this confusion, 
no doubt, is the dithculty of getting rij of the suspended clay, — 
ordinary filtration will not remove it. ( )b\iously all of the phos- 
])horus associated with the sus])ended clay should not l)e included 
with the organic phosphorus, altho part of it may l)e organic in 
form. Fraps renn)\ed the clay l)y precijjitation \\\\\\ ammonium 
suit ate. There is no evidence, however, that this reagent does 
not also precipitate some organic matter either chemically or me- 
chanically. Ammonium sulfate is used by physiological chemists 
to precipitate the proteins in order to make certain group separa- 
tions, while some preliminary work here show-ed that complete 
saturation of the ammoniacal extract of the soil with ammonium 
suit ate, alter the remo\'al of the suspended clay, produced a heavier 
([ualitativc prcci])itate of organic matter than did the addition of 
hydrochloric acid, ft would seem, therefore, that the evaporation 
method of Hampton and Alooers (yy) is more desirable for the 



ipiO] CaKBOX, PllOSl'llORUS AND NlTKOGEN IN SulLS 113 

removal of the suspended clay. Unless otherwise stated tlie latter 
method was used for the removal of the suspended clay in all the 
work reported in this paper. 

Owing to the contiictino- evidence regarding- the phosphorus as- 
sociated with the extracted iiiaticrc noire, it seemed desirahle to do 
some work with this material other than the simple determination 
of the phosphorus. 

The soil, \\ithout previous treatment with hydrochloric acid to 
remove the calcium, w^as extracted with 4 percent ammonia in the 
ratiO' of i part of soil to 50 parts of ammonia water for 36 hours 
as in the usual humus determinations. The clay was removed by 
evaporation and the iiiaticrc noire was obtained in quantity for 
study. Conditions here are such that the maximum quantity of in- 
organic phosphorus should be found in the ammoniacal extract 
since none has previously been remoxed l)v treatment with a min- 
eral acid as in the usual humus determinations. 

The suspended clay removed by evaporaticMi was analw.ed for 
carl)on and phosphorus with results as follows: Carbon ^.y;^ per- 
cent and 3.61 percent, or an average of 3.67 per cent; phosphorus 
o. 118 percent and 0.109 percent, or an average of o. 113 percent. 
Since the carbon in the original soil was only 2.09 percent wdiile 
the pho.sphorus was .046 percent, the relative increase of carbon 
and phosphorus in the suspended clay indicates undoul)tedly the 
accumulation of organic matter with the "clay." It would appear 
probable that the grinding of the sample of soil, while preparing 
it for analysis, would con\ert the organic matter into an im- 
palpable powder wdiich would ha\e a tendency to remain sus- 
pended in the li(|uid tog'ether with the fine clav particles when the 
soil was extracted with ammonia. 

The amount of the extracted niaticrc noire \\as determined. 
It was then analyzed for carlion, nitrogen, and |)hosphorus. The 
carbon was determined b\' the method suggested by Pettit and 
Schaub (59). The total nitrogen was determined by the regular 
Kjeldahl method ; correction was then made for the absorbed am- 
moniacal nitrogen by determining the latter in a separate sample 
by distillation with magnesium oxide. The phosphorus was de- 
temiined by igniting a sample of the inatiere noire and treating 
the ash with aqua re.gia; the silica was removed bv evaporation 
and the phosphorus determined bv the usual \olumetric method. A 
confirmatory test made by detennining phosphorus l)y fusion with 
sodium peroxid gave 0.835 percent and 0.815 percent phosph(M-us 
in the inatiere noire while the method adopted ga\e 0.860 percent 
and 0.830 percent. 

The results obtained expressed as poiuids per two nn'llion 
pounds of soil are recorded in Table 17. 



114 



Bulletin No. 145 



[Atnl, 



Tablk M.—Mafihr A'ain-, Carbon, Nitkogkn and Phosphorus in the 
MatierE Noire; Resui.ts Expressed as Pounds per two 
Million Pounds ok Dry Soil. 
(Soil not acid-extracted before treatment with ammonia) 



Number 


Matihr Noire 


Carbon in the 
Ufatihr A'oi'rr 


Nitrogen in 

the 

/l/afiar Noire 


Phosphorus 

in the 

jMatihr Noire 


A 
B 


27600 
28600 


10870 
10850 


1642 

1662 


233 
242 


Averag-e 


28100 


10860 


1652 


238 



Phosphorus-nitrog-en ratio = i :6.9 
Nitrogen-carbon ratio = i :<">.6 
Phosphorns-carl)oii ratio = i :45.6. 

The uiaiicrc noire was now redissolvcd in dilnte ammonia, an 
excess of i percent hydrocliloric acid added and set aside over 
night. The precipitate of organic matter was l)roiight on to a filter 
paper, which had previonsly been dried at itoX and weighed. 
The precipitate was washed with i percent liydrochloric acid, dried 
at iio°C and weighed. The precipitated iiiatirrc noire was olitained 
in ciuantity and analyzed for carbon, nitrogen and phosphorns. The 
resnlts obtained are recorded in Table 18. 

Table 18. -PercipiTaTEd Malivre Noire, Carbon. Nitrogen and Phos- 
phorus IN Precipitated 3fatihe Noire: Resuets Expressed as 
Pounds per Two Million Pounds ok Dry Soil 

(Soil not acid-extracted before treatmen t with ammonia) 



Number 


percipitated 
Matihr Noire 


Carbon in 

precipated 

Dfatiere Noire 


Nitrogen in 

precipitated 

Dfafilre Noire 


Phosphoru.s in 

precipitated 
ISIatilre Noire 


A 
B 


9174 
9203 


4262 
4303 


604 
628 


20 
18 


Average 


9189 


4282 


616 


19 



Phosphorns-nitrogen ratio = i :3J.4 
Nitrog'en-carbon ratio =1:7 
Phosphorus-carl)on ratio — i :jj5 

The results recorded in Tables 17 and iS are very significant 
as can be more readily seen by glancing at Tal)le 19 which sum- 
marizes the above data. 

Tabli: 19.— yi/a///;v' Noire, Carbon, Nitrogen and Phosphorus Precipi- 

tati';d From Ammoniacal Solution by Hydrochloric Acid: Results 

Expressed as Percent of Total Soluble in Ammonia. 

(Soil not acid-extracted before treatment with ammonia) 



Matiire Noire 


Carbon 


Nitrogen 


Phosphorus 


32.7 


39.4 


37.3 


8.0 



jpio] 



Carbon, PiiosnioRus and Nitrogen in Soils 



115 



Of the total maticrc noire obtained, only 32.7 percent has been 
precipitated from the alkaline solution by hydrochloric acid. The 
portion remaining in solution does not consist of inorg-anic salts, 
as might be supposed, as is readily shown by the fact that only 
39.4 percent of the carbon and 37.3 percent of the nitrogen has 
been precipitated. This shows conclusively that only about 1/3 of 
the dissolved organic matter has been precipitated. 

Only 8.0 percent of the total soluble phosphorus, or 19 pounds 
out of 238 pounds, has been precipitated from alkaline solution by 
hydrochloric acid. Has the phosphorus remaining in solution in 
the mother liquor been derived from organic or inorganic sources? 
The fact that 60.6 percent of the carbon and 62.7 percent of the 
nitrogen also remain dissolved in the mother liquor would appear 
to be significant. 

Having made a study of the maticrc noire obtained from the 
original soil it seemed desirable to investigate the niatierc noire 
obtained in the usual way after the soil had been extracted with 
I percent hydrochloric acid to remove the calcium and magnesium. 
It seemed reasonable to suppose that the acid extraction would re- 
move also a considerable quantity, if not all, of the inorg'anic phos- 
phorus, which may ha\e previously passed into the ammonia so- 
lution. 

As before, the amount of luaficrc noire was determined and 
then extracted in quantity for the determination of carbon, nitrogen 
and phosphorus. The results obtained will be found in Table 20. 

Table 20. — Matih-e Noire, Carbon. Nitrogkn and Pho.sphokus in the 

Mature Noire: Results Expressed as Pounds per Two 

Million Pounds of Dry Soil 

(Soil acid extracted before treatment with ammonia) 



Number 


3latiere Noire 


Carbon in the 
Matilre Noire 


Nitrogen in 

the 

ilfatihe Ao/;r 


Phosphorus 
in the 

Matiere Noire 


A 
B 


60840 
61660 


258(.0 
25790 


2805 
2885 


524 
508 


Averag^e 


61250 


25825 


2845 


516 



Phosphorus-nitrogen ratio ^ i :5.5 
Nitrogen-carbon ratio = i •.9.1 
Phosphorus-carbon ratio ^ i 150 



The maticrc noire was redissolved in dilute ammonia and an 
excess of i percent hydrochloric acid added. The amount of the 
precipitate and the carbon, nitrogen and phosphorus in the precipi- 
tate were determined as before. The results obtained are recorded 
in Table 21. 



116 



Bulletin No. 145 



[At HI, 



Tablk 21. — Pkkcipitatkd Malihc Noire; Cakbon, Nitkoc.kn and Pitospho- 

Kus IN THE Precipitated Mature Noire: Kesults Expressed as 

Pounds in Two Mii^lion Pounds of Dry Soil 

(Soil first acid-extracted before treatment with aminonia) 



Number 


Precipitated 
iMaiilrc N^oire 


Carbon in 

precipitated 

3/afih'e Noire 

11410 
11555 


Nitro<,''en in 

precipitated 

Matihe Noire 


Phosphorus in 

precipitated 
Matihe Noire 


A 
B 


■ 30110 
31140 


1242 
1198 


57 
56 


Average 


30()25 


11482 


1220 1 56 



Phosphorus-nitroo'en ratio = i :2\.y 
Nitrogen-carbon ratio = i X).'^ 
Phosphorus-carbon ratio =^ i 1205 

'I'ablc 22 summarizes the resuhs reported in Tables 20 and 21. 
()f llie total dissolved maticrc noire only 30 percent was precipi- 
tated. Again the greater part of the carbon and nitrogen remain 
in the mother li(|uor. Only 44.5 jiercent of the carbon and 42.9 
percent of the nitrogen were i)reci[)itated while Init 'S.'j percent of 
the phosphorus was precipitated. 

Table 22. — /Matii re Noire; Carbon, Nitrogen and Phosphorus Precipi- 
tated FKOM AmMONIACAL SOLUTION BV HYDROCHLORIC AciD: RESULTS 

Expressed as Percent of Total Soluble in Ammonia 
(Soil first acid-extracted before treatment with ammonia) 



Matih-e Noire 


Carbon 


Nitrogen Phosphorus 


50.0 


44.5 


42 . 9 8.7 



Again, the ([tiestion regarding the source of the phosphorus 
remaining in solution arises. It will be seen that 55.6 percent of 
the soluble carbon and 58. i percent of the soluble nitrogen also re- 
main in solution. Attentiou should l)e called to the fact that when 
the original soil was treated direct with ammonia, withotit previ- 
ous extraction with h\'(lrochloric acid, under conditions where the 
UL-Lximum amount of inorganic phosphorus should be dissolved, 
onl\" 23S ])ounds of phosphorus per tw'o million pounds of soil 
were obtained: \-et, after the soil had been treated with hydro- 
chloric acid to remove the calcium, under conditions where the 
minimum amount of inorganic phosphorus would be dissohed by 
ammonia, 516 pounds of phosphorus per two million pounds of 
soil were obtained. The difference between these two numbers, 
27S |)ounds, imquestiimably represents phosphorus which must have 
been derived from organic sources. Now% since only 55 potuids of 
phosj)horus is precipitated with the maticrc noire by hydrochloric 
acid, it \vould appear th.'it the organic phosphorus associated with 
the precipitated inoticrc noire is onlv a A-er\' small i)art of the or- 
ganic phosjihorus present in the soil. 



IQIO] 



Carbon, Phosphorus and Nitrogen in Soils 



117 



Schmoeger (39) has demonstrated that the organic phos- 
phorus compounds of the soil are decomposed by heating under 
pressure. It would appear probable, therefore, that the simple 
evaporation of the ammoniacal solution on the water bath in the 
preparation of the niatierc noire in quantity for analysis would 
cause a decomiwsition of the phosphorus compounds; hence when 
the niatierc noire is redissolved and precipitated by hydrochloric 
acid, less phosphorus w^ould be obtained in the precipitate than 
would be the case if the material had not been heated. This idea 
was confirmed by experimental evidence as is shown in Table 23. 
The precipitated matiere noire obtained from the original soil, 
which had not been extracted with hydrochloric acid, showed 19 
pounds of phosphorus per two million pounds of soil. A portion 
of the ammoniacal extract of this soil was freed from clay by 
Frap's method; an aliquot part of the extract was then neutralized 
with hydrochloric acid : the precipitate obtained showed 68 pounds 
of phosphorus per two million pounds of soil, or over three times 
as much as did the precipitate obtained from the evaporated ma- 
terial. 

Table 23. — Phosphorus in Precipitated Matih-e Noire: Results Ex- 
pressed AS Pounds per Two Million Pounds of Dry Soii, 





Soil not acid-extracted 


Soil acid-extracted 


Number 


Phosphorus 

in heated 
MatiereNoire 


Phosphorus 
in unheated 
ISIatureNoire 


Phosphorus 

in heated 
Matih-cNoire 


Phosphorus 
in unheated 
MatureNoire 


Phosphorus 
in barium 
precipitate 


A 
B 


20 
18 


61 

77 


56 

57 


133 
164 


133 
138 


Averag-e 


19 


69 


M> 


149 


135 



The acid extracted soil gave similar results : the precipitated 
matiere noire which had been subjected to heat gave only 55 
pounds of phosphorus per two million pounds of soil, while the 
precipitated matiere noire which had not been subjected to heat 
gave 149 pounds or nearly three times as much. The latter result 
was again confirmed. When the ammoniacal extract, freed from 
clay by precipitation with ammonium sulfate, is treated with 
barium chloride, the organic matter is quantitatively precipitated 
as is indicated l)y the decolorizing of the supernatent liquid and by 
the fact that evaporation of the filtrate and ignition of the residue 
gives only a veiy faint charring. But unfortunately the barium 
chloride also precipitates the inorganic phosphorus as barium 
phosphate under these conditions, and when the liquid is rendered 
acid it becomes colored, showing that organic matter as well as 
inorganic phosphorus has been dissolved. However, the precipi- 
tate was separated by filtration, washed with hydrochloric acid un- 



118 Bulletin No. 145 [April, 

til free from barium and the phosphorus determined. This phos- 
phorus must have been derived from orj^'anic sources. The resuUs 
are recorded in the hist cohimn of Table _'3 and compare very well 
with those previously ol:)tained. 

According- to Scl'imoe.ger, extraclinu of the soil for 24 hours 
with 12 percent cold hvdrochloric acid removes all of the inorganic 
phosphorus readilv soluble in dilute acids. W'tmld not such treat- 
ment also remo\e an\- in(»rganic phosphorus readil}' soluble in 
dilute alkali" It would certainly seem that the subsc<iuent extrac- 
tion W'ith dilute ammonia of the acid extracted residue ouo-ht to 
dissolve onlv organic ph(jsphorus. This idea was conhrmed by ex- 
perimental c\idence and thus additional information regarding- the 
nature of the ammonia-soluble phosphorus was obtained. 

Two samples of 10 grams each of the soil under consideration 
were extracted for 24 hours with 100 c.c of \2 percent cold hydro- 
chloric acid, then tfltered and washed with hot water until the fil- 
trate was free from chlorides. One of the samples was then 
extracted with 4 percent ammonia for 36 hours in the usual wa}' 
and the amount (jf ammonia-soluljle i)hosphorus determined: the 
second sample was again extracted with 1 _' ])ercent cold hydro- 
chloric aci<l t'or ]() hours and the amount of soluble j>hosi)horus 
determined. Txtth experiments were du])licate(l. The dilute am- 
monia extracted 540 and ~^jo pounds of i)bos])liorus or an ax'erage 
of :;:^c^ pounds of pliosphorus per twc^ million pounds of soil which 
had previouslv l)een extracted with cold ij percent hydrochloric 
acid, \vhile a second extraction with cr)ld i_> percent hydrochloric 
acid yielded ouh' (^4 and 96 jiounds or an average of 95 pounds of 
phosphorus per two million pounds of soil. 

It would seem reasonable to suppose that both extractions of 
the soil with cold \2 ])ercent hydrochloric acid removed some 
organic ])lios])li(ii-us since llerthelot and .\ndre (31) have dennni- 
strated that organic matter ()\ the soil is somewhat soluble in this 
reagent. 

It would also seem \er\- inircusoiialilc to suppose that dilute 
ammonia ]iossessed as g-reat a solvent power iov inorganic phos- 
phorus as does 12 percent cold hydrochloric acid. But, assuming, 
for the sake of argument, that oul\' inorganic phos])horus is ex- 
tracted l)v the lu'drochloric acid and that dilute ammonia has as 
great a sohent power for iuorg'anic phos])h()rus as the hydr(")chloric 
acid, the alxive exi)eriments seem tc) demonstrate that at least 
4O0 ])i)unds of ])hosphorus iSSS''^)?'^ "^ ^^^*^ ammonia-soluljle phos- 
])horus has been (leri\-e(l from organic sources and that at least 
J^.^ ]vercenl of tlie ammonia-soluble i)hos])borus has been derived 
1 rom organic sources. 



iQio] Carbon, Phosphorus and Nitrocen in Soils 119 

(c) ORGANIC PHOSPHORUS BY SCHMOKGKr'S METHOD 

The second method for determining- the organic phosphorus is 
the one proposed hy Schmoeger. Eg'gert, Nilson, Tache and others 
have shown that simple ignition increased the sohil>ihty of the 
phosphorus in cold hydrochloric acid. The increased solubility of 
the phosphorus was believed to be due to the destruction of the 
org'anic phosphorus compounds. Therefore, the amount of phos- 
phorus in the original soil, soluble in cold hydrochloric acid, sul>- 
tracted from the amount in the ignited soil soluble in cold 
hydrochloric acid of the same strength was reg'arded as having 
been derived from the organic phosphorus compounds. This as- 
sumption was confirmed by Schmoeger by hydrolyzing- the soil un- 
der pressure at a temperature of i40°-i6o°C. This treatment of 
the soil decomposetl the organic phosphorus compounds so that the 
organic phosphorus was rendered soluble in cold hydrochloric acid. 
The difference, therefore, between the amount of phosphorus ex- 
tracted from the original soil by cold hydrochloric acid and the 
amount extracted from the soil which had been hydrolized gave the 
amount of organic phosphorus. Schmoeger found that, as a rule, 
concordant results were obtained by the two methods altho in cer- 
tain cases slightly higher results were obtained by the latter method. 

It was decided to determine the organic phosphorus bv both of 
the above methods. Thus, lo grams of the orig-inal soil was 
treated with lOO c.c. of 12 percent hydrochloric acid and digested 
in the cold with an occasional shaking for 24 hours. A second 
sample of 10 grams was ignited and then extracted with 12 percent 
cold hydrochloric acid in a similar manner. .Vt the end of 24 hours 
the extract was diluted with water and separated by filtration. The 
residue was washed with cold water until the filtrate was free from 
chlorides: the filtrate was then made up to 500 c.c. and 100 c.c. 
used for the phosphorus determination. The results recorded in 
Table 24 show that there are 271 pounds of phosphorus in the 
original soil solulile in 12 percent cold hvdrochloric acid while 
there are 814 poun.ds in the ignited soil solul)le in the same reagent. 
These results show, therefore, that there are 543 pounds of organic 
phosphorus in two million pounds of the surface soil. 

Another sample of 10 grams of the soil was treated with acidu- 
lated water and heated in an autoclave for 12 hours at a tempera- 
ture of I40°-I45°C. The sample was then digested for 24 hours 
with cold hydrochloric acid, filtered and the filtrate made up to 
500 c.c. An a\"erage of two determinati()ns show that 878 poimds 
of phosphorus were obtained. This would indicate that there were 
607 pounds of organic i)hos|)horus in two million ])ounds of the 
surface soil. Sliglul}- higher results for organic phosphorus are thus 



120 



Bulletin No. 145 



[April, 



obtained Ijy the autoclaA'e method but it is probably more nearly 
correct since it is difticiilt to conceive how the treatment in the 
autoclave would render any inorganic phosphorus soluble which 
would not be rendered soluble l)y io-nition while the work of Leav- 
itt and LeClerc (81, 82) would indicate that ignition might render 
some of the organic [)liosi)hurus insoluble in cold hydrochloric acid 
of any strength. 

The calculation method shows that 423 pounds of phosphorus 
per two millions of the surface soil are in organic combination: 
the ammoniacal extraction method shows 504 pounds of organic 
phosphorus and the ignition method shows 543 pounds, while 

T.\BLK 24.— Phosphorus Soluble in Twelve Percent Hydrochloric Acid: 
Results Expressed as Pounds in Two Million Pounds ok Soil 



Number 


Original 
soil 


Ignited 
soil 


Organic 
phosphorus 


A 
B 


26(1 
276 


819 
809 




Average 


271 


814 


543 



Table 25. — Phosphorus Soluble in Twelve Percent Hydrochloric Acid: 
RivSULTs Expressed as Pounds in Two Million Pounds oe Soil 



Number 


Original 

soil 


Evaporated 
soil 


Organic 
phosphorus 


A 
B 


266 
276 


876 
880 




Average 


271 


878 


607 



Schmocger's mctliod shows that there are 607 pounds of organic 
phosphorus. The calculation method is, therefore, very conserva- 
tive in nature and it can be safely stated that at least that much 
phosphorus is in organic combination. Tal)le 26 gi\es the sum- 
marized results of 1I1C organic ])hosphorus ol)tained bv the several 
methods. 



Table 26. — Total Phosphorus and Organic Phosphorus by Several 

Methods 





Organic phos- 
phorus by cal- 
culation 


Organic phos- 
phorus by solu- 
tion in dilute 
ammonia 


( )rganic phos- 
phorus by ig- 
nition 


Organic phos- 
phorus by evap- 
oration 
(Schmoeger) 


Total 

l)hos- 

phorus 


Pounds 
per two 
million 
pounds 
of soil 


Per- 
cent of 
total 


Pounds 
per two 

million 
l)Ounds 

of soil 


Per- 
cent of 
total 


Pounds 

per two 

million 

pounds 

of soil 


Per- 
cent of 
total 


Pounds 
per two 
million 
pounds 
of soil 


Per- 
cent of 
total 


919 


423 


46 


504 55 


543 60 


607 66 



/p/o] Carbon, PHOsruoRUs and Nitrogen in Soils 121 



CONCLUSIONS 

1. The phosphorus-nitrogen ratio in the surface soil of tlie 
brown silt loam soils is i :i3.5 while the same ratio in the black 
clay loam soils is i :ii.4. 

2. Under normal conditions the nitrogen-carbon ratio of the 
soil has a tendency to become narrower as the age of the organic 
material increases : the ratio, however, never becomes narrower or 
even e(|ual to the ratio of the more common proteins contained in 
the hunnis producing materials. 

3. The nitrogen-carbon ratios of the ordinary brown silt loam 
soils of Illinois are 1:12.1, 1:11.5 and 1:8.9 ^^^ ^^''^ surface, sub- 
surface, and subsoil respectively. 

The ratios in the black clay loam soils are i :ti.7, i :ii.9 and 
I :g in the surface, subsurface, and subsoil respectively. 

4. The phosphorus-carbon ratio in the surface soil of the 
browai silt loam is i : 165.2 while the ratio in the surface soil of the 
black clay loam soils is i : 163.6. 

5. The calculation method for determining organic phosphorus 
is very conservative in character and can be relied upon in drawing 
broad general conclusions. 

6. The evaporation on the water bath of the ammoniacal so- 
lution, in the preparation of the iiiaUcre noire in quantity for analy- 
sis, causes a hydrolysis of the organic phosphorus compounds. 

7. The determination of the phosphorus associated with the 
precipitated maticrc noire is not a quantitative method for the de- 
termination of the total organic phosphorus of the soil. It should 
be regarded only as a good qualitative evidence of the existence of 
organic phosphorus in the soil. 

8. The contention of Fraps that, "There is no evidence that 
the phosphoric acid in the filtrate is in organic combination" and 
that, "It is probably derived from the iron and aluminium phos- 
phates" is entirely untenable. 



iQio] Carbon, Phosphorus and Nitrogen in Soils 123 

BIBUOGRArHY 

1. MuLDivR, — L\'l)cr (lie liestandtlieile dcr Ackcrcrdc. Journal 
fiir praktische Chemie : ( i(S44), Band 32, S. 326. 

2. Wolff', — Zeitschrift fur Analytische Clieniic : (1864), Band 
3, S. loi. 

3. DeIvESSK, — Recherche de Tazote et des niatieres organiques 
dans les substances minerales. Compt. rend.: (i860) tome 
51, pp. 286, 405. 

4. MuLEER,— Gehalt der Ackererden an StickstotT. Die land- 
wirthschaftlichen Versuchs-Stationen : (1861), Band 4, S. 234. 

5. Thenard, — Note sur Taction recii)rog'ue des phosphates, de 
ramnioniaque et de divers corps neutres organicjues les uns sur 
les auters. Compt. rend.: (i860), tome 53, p. 1019. 

6. Thenard, — Considerations sur la formation de certains ma- 
tieres azotees et particulierement sur I'acide fumique. Compt. 
rend.: (1861), tome ^2, p. 444. 

7. ScHURTzENBKRGER, — Actiou de rammoniacpie causticjue sur 
les substances organi([nes. Compt. rend.: (1861), tome ^2, 
p. 641. 

8. BerthELOT, — Xoiuelles contriljutiuns a riiistorie du carbune. 
Compt. rend.: (1871), tome y^, p. 4(^4. 

9. Detmer, — Die Natiirlichen Humuskorper des Bodens und 
ihre landwirthschaftliche Bedeutung. Die landwirthschaft- 
lichen Versuchs-Stationen: ( 1871 ), IJand 14, S. 148. 

10. Grande Au, — Recherches sur le rcjle des niatieres organiques 
du sol dans les phenomenes de la nutrition des ^•egetaux. 
Compt. rend.: (1872), tome 74, p. c)HS. 

11. Simon, — Die Humuskorper in ihrer Beziehung zur Pflanzen- 
ernahrung. 13ie landwirthschaftlichen Versuchs-Stationen : 
(1875), Band 18, S. 45 -^ 

12. ScHUETz, — Ueber die vSteigerung- des Abs()r[)ti(jnsvermogens 
von Kaiserstuhler Basaltboden fue Phosphorsiiure durch misch- 
nng mit Humus. Hoffmamis Agrikultur-Chemie : (1876), 
Band 16, (old series) vS. loi. 

13. EiCHORN, — L'eber die Einvvirkung humus reicher Ei'den auf 
Salze besonders phosphorsauren Kalk. Landwirthschaftliche 
Jahrbiiche: (1877), Band 6, S. 957. 

14. PiTSCH, — Untersuchnngen fiber die dem Boden durch Al- 
kalien entziehbaren Humusstoffe. Die landwirthschaftlichen 
Versuchs-Stationen: (1881), Band 26, S. i. 

15. Gasparix. — Xote sur la dissemination rassimilation et la de- 
termination de I'acide phosphorique dans les terres arables. 
Compt. rend.: (1884), tome 98, p. 201. 



124 Bulletin No. 145 [-^pril, 

16. LawjvS and Gilbert, — On some Points in the composition of 
Soils, etc., etc. Journal of Chemical Society (London) : 
(1885), Vol. 47 f., p. 419. 

17. SosTKGNi, — F,inig-e Untersuclinn.gen iilier die aus Torf ge- 
winnenen Hnmuskorper. Die landwirthschaftlichen Versuchs- 
Stationen: (1886), Band 32, S. 9. 

18. BerThKLOT IvT Andre, — Snr les principes azotes de la terre 
veg-etale. Compt. rend.: (1886), tome 103, p. iioi. 

19. BerTiiElot, — Sur de dosage dn carbone organiqnc contenu 
dans les sols qui fixent I'azote lil)re. Compt. rend.: (1886), 
tome 102, p. 951. 

20. BertiiEEOT ET Andrk, — Sur I'etat du soufre et du phosphore 
dans les plants, la terre et le terreau, et sur leur dosage. Compt. 
rend.: (1887), tome 105, p. 1217. 

21. Ec.GERTz, — Studien und Untersuchung-en iiber die Ilumus- 
korper der Acker-und Moorerde. Biedermanns Central-blatt 
fiir Ag-rikulturchemie: (1889), Band 18, S. 75. 

22. DehERAIn, — Dur I'epuisement des terres par la culture sans 
eng-rais et Tutilite de la matiere org-anique du sol. Compt. 
rend.: (1889), tome 109, p. 781. 

23. Van BemmeeEn, — Die Zusammenstezung der Ackererde, 
nacli Anleitung- der in dem vorigen Abhandlungen mitgeleiten 
Analysen von gewolmlichen und vulkanischen Thonboden. 
Die landwirthschaftlichen Vcrsuchs-Stationen : (1890), Band 

37, vS. 347- 

24. KosTYTSCHiFE, — Reclicrchcs sur la formation et les ([ualites 
de riuimus. Annales Agronomique : (1890), tome 17, p. 17. 

2S- WiKLUND, — Ueber die Phosphors;iiu"e im Moorboden und ihrc 
Bestimmung. Landwirthschaftliche Jahrlnicher: (1891), 
Band 20, Heft 4, S. 909. 

26. BerthEEOT et Andrk, — Reclicrches sur les substances humi- 
ques. Compt. rend.: (1891), tome 112, p. 916. 

27. BerthEEOT et Andrk, — Sur le dosage des maticres minerales 
contenues dans la terre vegTtale et sur leur role en Agrikulture. 
Annales de Chemie et de Physique: (1892), tome 25, sixieme 
serie, p. 289. 

28. Snyder,— The Composition of Native and Cultivated Soils 
and the Effects of Continuous Cultixation upon their Fertil- 
ity. Minn. Exp. Sta. : (1892), Bui. 30, p. 165. 

29. vSciiMOEGER, — Ueber den Phosphor in Moorboden. Berichte 
der Deutsche Chemischen Gesellschaft : (1893), Band 26, 
Heft I, S. 386. 

30. HiEC.ARD and JaFI'A, — On the Nitrogen contents of Soil Hu- 
mus in the Arid and Humid Regions. Calif. Sta. Rept. 1892- 

93- 



/p/Oj 



Carbon, Phosphorus and Nitrogen in Soils 125 



31. BerthELOT ET Andre,' — Sur les matiere coiistitutives du sol 
vegetal. Compt. rend.: (1893), tome 116, p. 666. 

32. Demoussy, — Investigations at Grignon Station. Exp. Sta. 
Record: (1893), Vol. 5, p. 18. 

33. TackE; — Ueber eine eigentiimliche Eigenschaft der Phos- 
phorsaure im Moorboden. Biedernianns Central-blatt fur 
Agrikulturchemie : (1894), Band 24, S. 82. 

34. Snyder, — Notes on the Grandeau Method for the Determina- 
tion of Humus of Soils. Jr. Am. Chem. Soc. : (1894), Vol. 
16, p. 210. 

35. Jaeea, — Investigations of Matiere noire or Humus. Calif. 
Agr. Exp. Sta. Rept. 1894-95, p. 35. 

36. Snyder, — Humus as a Factor of Soil Fertility. Minn. Agr. 
Exp. Sta. : (1895), Bui. 41, p. 23. 

37. Snyder, — Production of Humus from Manures. Minn. Agr. 
Exp. Sta.: (1896), Bui. 53, p. 12. 

38. FuEMER, — Some Notes Concerning the Nitrogen Content of 
Soils. Wash. Agr. Exp. Sta. : (1896), Bui. 23, p. 17. 

39. ScHMOEGER, — Untersuchungen fiber einige Bestandteile des 
Moores. Biedermanns Central-blatt fiir Agrikulturchemie: 
(1897), Band 26, S. 579- 

40. ScHMOEGER, — Sind die im Moor vorhandenen durch starhe 
Sauren nicht extrahierbaren Phosphor — und Schwefel — ver- 
bindungen bereits in den Moorbildenden Pflanzen enthalten? 
Landwirthschaftliche Jahrbiicher : (1897), Band 26, S. 549- 

41. Snyder, — The Composition of Humus. Jr. Am. Chem. Soc: 
(1897), Vol. 19, p. 738. 

42. TachE, — Die Arbeiten im Laboratorium der Station in Bremen 
und die Feld — und Wiesenversuche in den hremischen Mooren. 
Biedermanns Central-blatt fiir Agrikulturchemie: (1897), 
Band 26, S. 366. 

43. Ladd, — Soil Humus. North Dakota Agr. Exp. Sta.: (189S). 
Bui. 32, p. 272. 

44. Ladd, — Soil Studies. North Dakota Agr. Exp. Sta.: (1899), 
Bui. 35, p. 310. 

45. Hess, — Effects of various Systems of Fertilizing upon the 
Humus of the v^oil. Pa. Agr. Exp. Sta. Rept.: (1899-1900). 

p. 183. 

46. Ladd, — Humates and Soil Fertilitv. Jr. Am. Chem. Soc. : 
(1898), Vol. 20, p. 861. 

47. Andre, — Repartition du carbone dans les matieres humiques. 
Compt. rend.: (1899), tome 128, p. 513. 

48. WhEEEER,^ — The Amount of Humus in Soils and the Per- 
centages of Nitrogen in the Humus, etc., etc. Jr. Am. Chem. 
Soc: (1899), Vol 21, p. 1032. 



126 P.ur.LETiN No. 145 [Af^ril, 

49. NannKS, — Ziir Gralje ul)cr die Vei"l)iii(lun,^;"stormen der Phos- 
phorsiiure in der Moorerde. Jalires1)richt iiljer Agrikultiir- 
eheniie : ( 1899), Band 42, S. 89. 

50. SnvdKR,- — Availal)le IMant-food of Soils. Alinn. Agr. Ivxp. 
Sta. : ( 1900), lUil. 65, p. 61. 

51. Pagnol'L, — 1 Inniiis and Carl)on in Cnltivaled Soils. Exp. 
Sta. Record: (1900), Vol. 13, p. ui. 

32. Emmeri.ing, — Ueber die verscliiedenen Fornien der Phos- 
l)horsanre im lioden nnd deren Bestimnuing. Biedermanns 
Cenlral-blatt fin" Agrikultnrcliemie : ([900), Band 29, S. 75. 

53. IviMBACii, — Investigations on the Determinations and Compo- 
sition of Hnmus and its Nitrification. Jr. Am. Chem. Soc. : 
( 1900), Vol. 22, ]). 695. 

54. 1'rkar and Hi^ss, — Effects of Dift'erent Systems of Mannring 
L'jion the Amonnt and Onality of the llnmns in the S(m1. Pa. 
Agr. Exp. Sta. Kept. ( 1900-01 ), p. 173. 

55. Dvi'lu, — Resnits of Investigations on Rothamsted Soils. (3f- 
fice of Experiment Stations: ( 1902), IU1I. lof), p. 29. 

5O. l>ol\RENK(^ — Der Stickstoft' des Humus. Landwirthschaft- 
lichen Versuchs-Stationen : (1902), Band 56, S. 311. 

^j. Xaoaoka, — ( )n the effects of Soil Igniiion ni)on the availabil- 
ity of l'hosi)horic Acid. ]\x[). Sta. Record: ( [904), Vol. 16, 

P- 555- 
58. i\so, — Leber das Vorkommen von Phosphorsaure in (^rgan- 

ischen Verbindungen im Bioden. Biedermanns Central-blatt 

fiir Agrikulturchemie : (i(;04), Band 34, S. 3. 
5(). PiCTTiT and vSciiAL^B, — The Determination of Org"anic Carbon 

in Soils. Jr. Am. Chem. Soc: ( 1904), Vol. 26, p. 1640. 
60. PlAirrVsKiJ, and l\i".i-Uo(u;, — The IMiosphorus associated with 

the Organic Matter of tlie v^oil. Rhode Island Agr. Exp. Sta. 

Rept. ( 1904-05 ),. p. 2()H. 
()]. CamI'Rox and 1 >ri; \zi:ai,i;, — The Organic Matter in Soils and 

Sulisoils. jr. Am. Chem. v^oc. : (1(^04), Vol. 2(), p. 29. 
()2. Di'MONT, — Sur les engrais ]uimi(|ues complets. Compt. rend.: 

( 1904), tome 138, p. I42(^. 
()7,. Cameron, — A Comparison of the ( )rganic Matter in Dift'erent 

Soil Ty])es. Jr. Am. Chem. Soc: ( H)0~,), Vn\. 2~, p. 256. 
64. Dr.MoxT, — v^ur la \aleur agricole des matieres humi(iues. 

Compt. rend.: ( 1905), tome 140, p. 2^<k 
()^. hiMoNT, — Les comjKJses phospho-humi(|nes du sol. Compt. 

rend.: ( KjoC)), tome 143, ]>. 186. 
66. Hai.e and Mieei^r, — Tlie Xitr(»gen Comiiounds of the Eunda- 

menlal Rocks. The journal of Agricultural Science: ( 190S), 

Vol- ^, p. 343- 



i(^w] Carbon, Phosphorus and Nitrogen in Soils 127 

67. KoNiG, HasenbaumEr and Grossmann, — Das Verhalten der 
organisclien Siil>stanz des Bodens und der osmotische Driicb 
desselben. Die landwirthscbaftlichen Versuchs-Stationen : 
(1908), Band 69, S. 28. 

68. Hopkins and Pettit, — The Fertility in Illinois Soils. 111. 
A§-r. Exp. Sta. : (1908), Bui. 123, p. 204. 

69. Fraps, — The Ammonia-Soluble Phosphoric Acid of the vSoil. 
Am. Chem. Journal: (1908), Vol. 39, p. 579- 

70. D'UeTra, — Humus in Soils. Exp. Sta. Record: (1900), 
Vol. 12, p. 7^2. 

71. Hiegard, — Fruit and Fruit Soils in the Arid and Humid Re- 
gions. Calif. AgT. Exp. Sta. Rept. : (1892-93), p. t,2/. 

yz. Snyder, — Combinations of Humus .with Phosphates of the 
Soil. Minn. Agr. Exp. Sta.: (1904), Bui. 89, p. 205. 

yT). Hiegard. — Some Peculiarities of Rock-weathering and Soil 
Formation in the Arid and Humid Regions. The American 
Journal of Science: ( 1906), Vol. 21, Series 4, p. 261. 

74. Andre, — Sur la constitution des matieres humiques naturelles. 
Compt. rend.: (1898), tome 127, p. 414. 

75. Berth EEOT ET Andre, — Sur les principles azotes de la terre 
vegetale. Ann. Chim et Phys. : (1887), sixieme serie, tome 

II, P- 3f>8- 

76. Bertheeot et x\ndrk, — Faits pour servir a Thistorie des 
principles azotes renfermes dans la terre vegetale. i\nn. Chim. 
et Phys.: (1892), sixieme serie, tome 25, p. 314. 

yy. MooERS and Hampton, — The Separation of Clay in the Esti- 
mation of Humus. Jr. Am. Chem. Soc. : (1908), Vol. 30, 
p. 805. 

78. vSl'zU'KI, — Studies on Humus Formation. Chemical Abstracts: 
( 1908), Vol. 2, p. 570. 

79. Eggertz und NiESON, — Chemishe Untersuchung von Moor 
und Torfboden. Biedermann Central-l)latt fi_u- Agrikultur- 
chemie: (1889), Band 18, S. 664. 

80. Stoddart, — Soil Acidity in its Relation to Lack of Available 
Phosphates. The Journal of Industrial and Engineering 
Chemistry: (1909), Vol. i, p. 71. 

81. Leavitt and LeCeERC, — Loss of Phosphoric Acid in .\shing 
of Cereals. Jr. Am. Chem. Soc: (1909), Vol. 30, p. 391. 

82. Leavitt and LeClERC, — Determination of Phosphorus in Ash 
Analysis. Jr. Am. Chem. Soc: (1908), Vol. 30, p. 617. 



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